Rainbow Electronics U3741BM - Manual (Page 6)

6
U3741BM
4662B–RKE–10/04
Figure 3. Input Matching Network with SAW Filter
Figure 4. Input Matching Network without SAW Filter
Please note that for all coupling conditions (see Figure 3 and Figure 4), the bond wire
inductivity of the LNA ground is compensated. C3 forms a series resonance circuit
together with the bond wire. L = 25 nH is a feed inductor to establish a DC path. Its
value is not critical but must be large enough not to detune the series resonance circuit.
For cost reduction, this inductor can be easily printed on the PCB. This configuration
improves the sensitivity of the receiver by about 1 dB to 2 dB.
IN
IN_GND
OUT
OUT_GND
CASE_GND
B3555
U3741BM
C3
22p
L
25n
C16
100p
C17
8.2p
L3
TOKO LL2012
27NJ
27n
C2
8.2p
L2
TOKO LL2012
F33NJ
33n
1
2
3, 4 7, 8
5
6
8
9
RF
IN
f
RF
= 433.92 MHz
LNAGND
LNA_IN
IN
IN_GND
OUT
OUT_GND
CASE_GND
B3551
U3741BM
C3
47p
L
25n
C16
100p
C17
22p
L3
TOKO LL2012
F47NJ 47n
C2
10p
L2
TOKO LL2012
F82NJ
82n
1
2
3, 4 7, 8
5
6
8
9
f
RF
= 315 MHz
LNAGND
LNA_IN
RF
IN
U3741BM
15p 25n
100p 3.3p
TOKO LL2012
F22NJ
22n
8
9
RF
IN
f
RF
= 433.92 MHz
LNAGND
LNA_IN
U3741BM
33p 25n
100p 3.3p
TOKO LL2012
F39NJ
39n
8
9
RF
IN
f
RF
= 315 MHz
LNAGND
LNA_IN